Monitoring Problems, Cant pan left and right using audio out? Options

[ziprrr]

I just purchased a set of Tannoy active monitors for using with Logic and Garageband they sound awesome, but I have hooked them up to my mixer a Beringer Eurorack, everything sound fine but when I try to pan an instrument or vocal in Garageband or Logic it wont! It seems to stay all in the middle. Im going from the MAC G5 line out mini jack to a split 3/4 inch L&R jack in my mixer which says mono on the l&r inputs, but I have a set of Creative 5.1 surround speakers for use with Video editing using the optical in on my G5 and I can pan left and right when I use them with Garageband or Logic what am I doing wrong?